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Bear in mind that the access protection given by the community mechanism in the SNMP
V.1 is only very limited since the data, the MIB IDs and the communities are not encrypted
in the UDP data blocks of requests and responses as they are transmitted.
Deleting rows in tables using SNMP
SNMP itself has no mechanisms intended for deleting. You therefore have to use a trick
to delete entries from tables.
If you need to delete a row, you have to change the index entry value, i.e. the value in the
first column, to its current value.
Example: You want to delete the 3rd row from following IP routing table.
The entry '10.0.0.0' (i.e. the first cell of the third row) is amended in the manager to
its current value, i.e. to '10.0.0.0', and the Set command is sent off. The
SNMP SetRequest now contains the command to amend the first cell of the third
row to '10.0.0.0'. The SNMP software recognizes that this assignment to the index
is redundant and interprets it as a delete command.
Appending rows to tables using SNMP
There are two ways of inserting rows in a table:
Using the set command will result in a new row through setting a new index entry.
By using the command in the syntax:
someTable.1.2.2 = xyz
a row with index '2' will be generated in the table 'someTable', with the entry 'xyz'
in its second column. The '1' after the table name is constant for this command and
stands for 'someEntry' in the SNMP-Syntax.
When using SNMP managers that do not allow the entry of index values, it is
possible to amend any existing index entry to the new index value of the new row.
The row which has been used as the source for the amendment will itself remain
unchanged.
If we take Castlerock SNMPc as an example, the first possibility can be realized as
follows:
ቢ Activate the Display MIB Table item in the Manage menu of Castlerock SNMPc.
IP address IP-netmask Router name Distance
192.168.0.0 255.255.0.0 0.0.0.0 0
172.16.0.0 255.240.0.0 0.0.0.0 0
10.0.0.0 255.0.0.0 ROBERT 0
224.0.0.0 224.0.0.0 0.0.0.0 0